What Is a Drain-Waste-Vent System (DWV)?


Reviewed by: Hady Makhmalbaf Ph.D., PE, Sr. Mechanical Engineer

A DWV, or drainage, waste, and vent system assists in moving wastewater out of your home and preventing sewage backups. Understanding how the DWV works and what components are involved can help you troubleshoot any problems that may occur with your own plumbing. In this blog post, we’ll discuss what a DWV system is, the different components involved, and how to troubleshoot problems with this system.

What is a DWV system in plumbing?

DWV stands for Drainage, Waste, and Vent system. It is a key component of the building drainage system that collects wastewater from sinks, bathtubs, showers, and other fixtures in the home and sends it to the septic tank or sewer line.

The DWV system is basically a series of smaller piping components that get connected to each other in order for wastewater from the fixtures to drain into the waste line. There are three types of DWV piping, namely:

  • Drainage systems – this system collects used water through sinks and tubs and carries it to the main sewer line or septic tank.
  • Waste systems – this system collects wastewater through the lower portion of the building and carries it to the main sewer line.
  • Vent systems – this system brings in air to the drainage and waste lines so that wastewater can flow freely without any blockage.

DWV piping can be made of different materials, depending on what’s more practical for your particular application. For example, PVC DWV piping is used for basement applications where there’s a high level of moisture. Galvanized steel piping is widely used for waste lines because it can be easily attached to fittings and fixtures. Also, in high-rise buildings, galvanized steel can handle the pressure of water from several floors above. ABS DWV piping is another popular choice because it meets building codes in most jurisdictions and is flexible enough so that it can fit into tight spaces.

How does a DWV system work?

The DWV system collects wastewater from the bathroom, kitchen, and laundry room fixtures that either send water down the drain or use water to carry waste away. This consists of vents, drains, and traps.

A vent, which is connected to the drain line, brings in the air so that wastewater can flow continuously without any blockage.

Without the presence of a proper plumbing vent, two things can happen:

1. The drainage will not happen properly.

2. The water in the U trap will be sucked into the drain, exposing the unsanitary gases to the living spaces.

A trap on the other hand collects water so that there’s a barrier between sewer gases and fixtures.

The most popular connection method between vent and waste lines is called “Stacked”. In this method, horizontal drainage is connected to a vertical pipe (a.k.a. stack) that allows the waste to flow downward. The top of the stack goes to the highest floor and eventually through the roof and is exposed to ambient air. Air can freely come to the stack and allow water displacement to take place.

Wastewater can either go through a septic tank or sewer line. This will depend on what kind of sewage disposal system is permitted in your jurisdiction. If you have a sewer line, wastewater will travel directly to more distant drainage systems outside of the house. If you have a septic tank, wastewater will flow into it and be processed there for a certain amount of time before going out to the drainage system.

Benefits of a Healthy DWV System

In other words, if an issue occurs in a well-designed and sized system, only the affected branch needs maintenance service. The other parts will continue functioning as they should.

Another benefit of having properly installed drainage plumbing is that it can help reduce your water/sewer expenses because your septic tank or sewer line will have an easier time processing wastewater. This means that wastewater will pass through faster, and you won’t experience the problem of sewage back-ups such as those associated with septic system failure or clay piping problems.

Since this is a key component of your home’s drainage system, it should be regularly inspected to ensure that there are no blockages or leaks.

Regular maintenance can also help prolong the life of your drainage system, which means that you won’t have to spend as much on repairs.

Signs that your DWV system needs professional attention

There are some tell-tale signs that your drainage system needs professional attention. If you notice sewage or water backing up into your toilets, sinks, or tubs, this is an indication that something may be wrong with the DWV piping in your home. Sewage usually has a strong smell and if it’s seeping out on the exterior of your home, this is a surefire sign that you need to get help from a professional ASAP.

Other signs of potential DWV problems include: poorly draining sinks, wet walls, meters running when none of the fixtures are being used, and clogged toilets. If the water in your toilet takes too long to flush or absorbs into the carpeting, this can mean there’s a problem with the drainage line.

There is a way to see if there is leakage. One old, yet efficient trick is to read the meter number over a fairly long period (overnight for example) and see if there have been any changes. Keep in mind no fixtures should be used to ensure the test results are valid.

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